A conventional pneumatic tire used in winter has sipes in land portions such as blocks and ribs. The sipes, which extend in the widthwise direction of the tire in a zigzag path, are provided at prescribed intervals in the circumferential direction of the tire. High on-ice performance is achieved by an edge effect arising from the sipes (see a patent document 1, for example).
In the above pneumatic tire, a technique of providing a shallow groove between zigzag sipes adjacent in the circumferential direction of the tire is employed in order to improve driving stability during turning on a wet road surface, the shallow groove communicating with the zigzag sipes (see a patent document 2, for example). Driving stability during turning on a wet road surface is enhanced by an edge effect arising from the shallow groove extending in the circumferential direction of the tire while a decrease in land portion stiffness is suppressed by reducing the depth of the groove to thereby suppress reduction of driving stability on a dry road surface.
However, the tire having a structure as mentioned above needs to use a tire mold which has a venthole for air release in each part of the inner surface of the tire mold corresponding to a part of a land portion sectioned by the sipes and shallow groove in order to prevent occurrence of curing trouble arising from an air pocket. Therefore, a lot of bentholes must be formed in the mold. As a result, a production time of the mold is consumed, which creates a problem of an increase in mold production cost.
There is also a problem of troublesome spew-trimming operation and a lot of waste from trimming, because tire producing processes include a process of trimming spews formed on the surface of a tire by rubber flown into bentholes, and when the bentholes increase, the number of the spews increases.
Patent Document 1: Japanese Patent Application Kokai Publication HEI 10-24707
Patent Document 2: Japanese Patent Application Kokai Publication HEI 11-321240